Growth of silicon nanowires offers the possibility of forming arrays with a large surface-to-volume ratio. These arrays can be used for chemical or environmental sensing, for electrical transduction, or for electron emission.
Bulk synthesis of semiconductor nanowires has been traditionally achieved using several variations of transition metal catalyzed techniques such as vapor-liquid-solid (VLS) synthesis. See, e.g., Kamins et al., J. Appl. Phys. 89:1008-1018 (2001) and U.S. Pat. No. 6,248,674. In standard vapor-liquid-solid (VLS) synthesis techniques used for producing silicon nanowires, each wire grows from a single particle of gold, cobalt, nickel or other metal. A vapor-phase silicon-containing species transported to the catalyst inside a high-temperature furnace condenses on the surface of the molten catalyst, where it crystallizes to form silicon nanowires.
Silicon nanowires produced by the standard VLS process are composed of a single crystal. In the standard process, the size of the catalytic particle controls the diameter of the nanowire grown from it. Thus, in order to obtain a uniform nanowire diameter distribution, monodispersed catalyst particles need to be created on a solid substrate. However, creation of nanometer size catalyst droplets is a non-trivial task. The nanoparticles can be formed by deposition techniques, such as chemical vapor deposition or physical vapor deposition. Although they can be registered to previously formed patterns, creating these pattern requires additional processing, usually involving costly lithography. In addition, conventional lithography processes cannot readily form nanoparticles of the desired small dimensions Thus, there is a need for improved methods of forming evenly spaced catalytic particles having dimensions in the nanometer range.